1. Field of the Invention
The present invention relates to a semiconductor device having a modified dielectric film and a method of manufacturing the same. More particularly, the present invention relates to a technique suitably applied to a semiconductor device having a laser-cut fuse and a method of manufacturing the same.
2. Description of the Related Art
An aluminum interconnect layer showing a high electric conductivity is used for power supply lines and signal lines formed as upper-layer interconnect lines in a DRAM device, and interconnect lines having a larger thickness have been employed recently from the viewpoint of reducing the access time. Generally, there is a tendency of adding redundant memory cells to DRAM devices for the purpose of accommodating an initial failure of any of the memory cells and a fuse is provided as part of the aluminum interconnect line to control the redundant memory cells. After a device test is completed on the function of the memory cells, some of the fuses are cut by means of a laser beam based on the results of the device test. FIG. 5 of the accompanying drawings schematically illustrates part of the interconnect layers of a known DRAM device.
Referring to FIG. 5, the semiconductor device 50 includes an element forming region 41 and a fuse forming region 42. In the element forming region 41, at least three interlayer dielectric films 12, 18, 25 and interconnect lines 16, 24, 31 of three layers are arranged alternately on a semiconductor substrate 11, and these interconnect lines 16, 24, 31 are connected together by plugs 20, 27. The interconnect lines 16, 24, 31 have a multilayer structure formed by sequentially laying a barrier metal layer 13, 21, 28, a metal layer 14, 22, 29, such as made of aluminum, and an anti-reflection layer 15, 23, 30. Low-electric-resistance interconnect lines are realized by using larger-thickness layers. For example, the interconnect line 31 typically has a thickness of 1.6 μm.
A passivation film 34 that is highly water-resistant is formed on the topmost interconnect line 31 and the interlayer dielectric film 25 to prevent water from entering to inside of the semiconductor device 50 and corroding the interconnect lines 16, 24, 31. A thick organic dielectric film 35 is formed on the passivation film 34 by coating resin and a subsequent heat treatment thereof to protect the semiconductor device 50.
A fuse 17 is formed in the fuse forming region 42. The fuse 17 is typically formed in the layer same as that of the interconnect line 16. In the process of manufacturing the semiconductor device 50, an etching process is conducted to expose the electrode pad of the interconnect line 31 after forming the organic dielectric film 35. In the etching process, the organic dielectric film 35, the passivation film 34, the interlayer dielectric film 25 and an upper part of the interlayer dielectric film 18 overlying the fuse 17 are removed and a fuse-cutting hole 36 is formed to facilitate the step of cutting the fuse 17 by means of a laser beam. The depth of the fuse-cutting hole 36 is so controlled as to allow the thickness D1 of the interlayer dielectric layer 18 remaining on the fuse 17 to have a predetermined value whereby the fuse 17 is assuredly cut.
For instance, JP-2004-134640A describes a semiconductor device having an interconnect layer and a fuse made of aluminum.
Meanwhile, in semiconductor devices such as the semiconductor device 50, a problem of degradation in the water-resistance capability of the passivation film 34 and corrosion of interconnect lines has been and is taking place because of the increased thickness of the topmost-layer interconnect lines 31 including the power supply lines and the signal lines. The problem occurs because, as the thickness of the interconnect line 31 is increased, a large stress arises in the passivation film 34 near the bottom of the interconnect line 31, whereby cracks may easily appear thereat during the heat treatment as indicated by reference numeral 51 shown in FIG. 5. Additionally, the coverage of the passivation film 34 is degraded as the thickness of the interconnect line 31 increases to aggravate the problem. As the water-resistance capability of the passivation film 34 is degraded, moisture may penetrate into the internal of the passivation film 34 in an anti-moisture test or the like.
The above problem may be solved by increasing the thickness of the passivation film 34. However, in semiconductor devices having a fuse to be cut by means of a laser beam, the total thickness of the dielectric films 18, 25, 34 that are formed to overlie the fuse 17 tends to have a larger range of variation as the thickness of the passivation film 34 is increased. Ten, the thickness D1 of the interlayer dielectric film 18 that is left on the fuse 17 after the etching process may have a larger range of variation. Thus, some of the fuses of such semiconductor devices may be left uncut. The range of variation of the thickness D1 may be reduced by reducing the etching rate for forming the fuse-cutting hole 36. However, this inevitably reduces the throughput of the process for manufacturing semiconductor devices.